High-speed shimmy, Speed wobble

Shayne Wissler writes:

So to what do you attribute the change in response. The materials in
the bicycle do not change their response but the rider is a great
variable with the ability of denial of facts.

You have an average ability in ad hominems. Perhaps that works with
most people you encounter. It doesn't work on me. You know, I can
do ad hominems too, and I think I do a better job of it when I want
to. For example, what possible motivation might you have for
wanting to blame the rider at every turn? Let's see, could it be
the fact that bicycle manufacturers pay you money to testify against
injured cyclists?

Interesting twist. Where do you get that notion? You might want to
cite such a case if you want to improve your credibility.

Nice dodge. So to what do you attribute the change in response,
considering that according to your recounting of the event, everything
was the same. You seem to want others to solve your problem.

But let's get back on subject. I only ask you to refrain from the ad
hominems and just present whatever scientific knowledge you might
have. If you have none then feel free to take your ad hominems
somewhere else--I'm not interested in your speculations about what
cyclist might have been shivering from what, or your psychologizing
about who might be in denial of what facts.

These considerations come from observed phenomena of riders who had
exactly these problems. You don't address why you believe these
assessments are invalid or not scientific. How about putting forth
some of your own ideas on the subject instead of attacking those that
have been proposed.

Some of my findings arise from the time that I designed automotive
suspension for racing and sports cars at Porsche, analyzing their
response and that of motorcycles and bicycles that have some common
problems such as shimmy.

The Tacoma Narrows Bridge is an apt example here. The bridge worked
fine in many circumstances. But there was one particular
circumstance where it failed. That was enough to call the bridge a
complete engineering failure. Civil engineers used it to learn from
past mistakes and not make them again.

Unlike your bicycle, the conditions were different. This was the
first time the bridge was subjected to a continuous wind of that
magnitude. Once it began to twist from lateral sway, it became an
oscillating air foil with angular pitch. This bridge has been dragged
into proofs of many unrelated phenomena by armchair experts. It does
not apply here.

A bike that works for most riders, or for most weight distributions,
or for most handlebar positions, etc., but has a drastic and
unpredictable failure mode at a particular speed etc., represents a
similar design failure.

Yes the bicycle's materials don't change. Neither did the bridge's
materials. But the conditions of the uses *do* change. And when
those conditions are in the realm of what the designer should
expect, and the bike does something radically wrong, there's
something wrong with the bike. You can't blame the rider because he
leans forward a little, or tightens his grip, and the bike starts to
radically vibrate. It may be good advice to recommend that, for a
vibrating bike, the cyclist do various things to accomodate, but
this is in order to compensate for defective behavior, not something
that the rider "should" have been doing all along.

I think Sheldon Browns item on left hand threads has some appropriate
words on this:

# Ignorant people outside the bike industry sometimes make the
# astonishing discovery that the way it has been done for 100 years is
# "wrong." "Look at these fools, they go to the trouble of using a
# left thread on one pedal, then the bozos go and put the left thread
# on the wrong side! Shows that bicycle designers have no idea what
# they are doing..."

Steering dampers and other anti shimmy devices have not found favor
among bicyclists because the problem is neither serious enough nor the
mechanisms an acceptable alternative in cost, weight, or convenience.

Jobst Brandt

Tom Paterson writes:

Yes the bicycle's materials don't change.

How about the pressure in the tires? The only time I ever had a bad
speed wobble was trying to get stopped after running over a
thumbtack on a Rockies descent (Rt. 82 to Difficult Campground
outside Aspen, probably about the usual 7% for Co. grades). Rode the
same bike/tires/etc. "many" times down that hill with no problem as
long as the tires were pumped up. Braking with a deflating front was
quite different.

That may be so, but we aren't talking about a flat tire here. Besides,
you didn't say whether your bicycle began to shimmy. I can imagine a
hissing leak can cause some consternation on a fast descent.

Jobst Brandt

On Wed, 01 Oct 2003 20:39:00 GMT, may
have said:

Werehatrack who? writes:

Remember, many, if not most riders will never experience the problem
at all, and most won't care about it as a result. For those that do
experince the shimmy, it will usually be infrequent, and solvable by
farily trivial means. Trying to throw big-tech solutions at it is,
in my opinion, a sure way to go broke.

We have seen shimmy in shopping carts as well as with older cars. The
first use of ball joint suspension (low friction) on VW (old beetle)
prototypes caused severe shimmy, after which the distance between the
joints was greatly enlarged to give high stiffness and move the
resonance out of the range that a wheel can follow.

The VW rear-drive vehicles were all susceptible to resonant shimmy,
and by 1961 they all had steering dampers, even the model 181 which
had a modified Type 1 front axle with wider joint spacing than the
Beetle. See below for more info.

This is basically
what smaller bicycle frames do in that their shorter main tubes have
greater torsional stiffness causing a frequency mismatch between wheel
oscillation frequency and energy stored between bound and re-bound.

Yes, that's the problem, in a nutshell.

By the way, in the VW, the steering damper became standard equipment
in 1958 (or thereabouts; it might have been a year or two either way)
while the front ends were still equipped with kingpins, and after the
design went to ball joints in 1966, the spacing of the joints never
changed. The diameter of the ball joint stems was changed once, but a
VW Beetle front end with ball joints of any year will shimmy violently
if the damper is bad or missing. Kingpin front ends had the problem
to a slightly lesser extent, but it was still serious enough to merit
the damper. When the damper was first introduced as factory standard
equipment, it was also made available as a retrofit kit for all prior
models due to customer complaints about the problem. The MacPherson
strut suspensions on the Super Beetles were not immune; they, too, had
(and needed) a damper. (I was a VW dealer parts manager from 1981 to
1985, and had been in the VW parts business since 1973.)

All fames that I have ridden were larger than 24" (crank CL to CL of
horizontal top tube measured along the seat tube) and all shimmied on
demand (no hands with pedals at top and bottom of stroke) at speeds
over 22mph. This has not interfered with years of bicycling, at any
speeds over all terrain. As I see it, the main problem lies in riders
who do not understand what reinforces the phenomenon and whether their
bicycles are prone to that response in the first place.

I quite agree, although since I've experienced the problem far less,
it's much easier for me to ignore. At high speeds, I simply don't
take both hands off the bars, so I guess my habits have shielded me
from having to deal with the effects.

Crashing as a result of this is much like diving from the bicycle when
the chain skips. This is not an unmanageable phenomenon.

Unwanted, but as you say, not unmanageable.

--
My email address is antispammed;
pull WEEDS if replying via e-mail.
Yes, I have a killfile. If I don't respond to something,
it's also possible that I'm busy.

On Wed, 01 Oct 2003 16:28:14 -0400, Rick Onanian
may have said:

On Wed, 01 Oct 2003 20:10:40 GMT, "Shayne Wissler"
wrote:
Why get out of bed in the morning? Maybe you'll miss an important call
saying that you won the lottery.

Drat! I KNEW there was a reason I haven't yet won...it's because
I keep getting out of bed in the morning!

Dontcha just love people who scream "There's a problem here, and
somebody needs to fix it!", but who get all huffy when the answer is,
"Okay, go ahead."

--
My email address is antispammed;
pull WEEDS if replying via e-mail.
Yes, I have a killfile. If I don't respond to something,
it's also possible that I'm busy.

On Wed, 01 Oct 2003 21:36:17 GMT, may
have said:

Steering dampers and other anti shimmy devices have not found favor
among bicyclists because the problem is neither serious enough nor the
mechanisms an acceptable alternative in cost, weight, or convenience.

That's pretty much what I had suspected. (I had tried, as a mental
exercise, to come up with a clean way to retrofit one, and nothing I
could think of was without drawbacks that I found unacceptable.
Possible, yes, certainly; worth the effort and side effects, no, I
don't think so.)

--
My email address is antispammed;
pull WEEDS if replying via e-mail.
Yes, I have a killfile. If I don't respond to something,
it's also possible that I'm busy.

On Wed, 01 Oct 2003 22:15:04 GMT, Werehatrack
may have said:

The VW rear-drive vehicles were all susceptible to resonant shimmy,
and by 1961 they all had steering dampers, even the model 181 which
had a modified Type 1 front axle with wider joint spacing than the
Beetle. See below for more info.

Of course, the model 181 didn't go into production until 1972 IIRC,
but it had a damper, and it needed one.



--
My email address is antispammed;
pull WEEDS if replying via e-mail.
Yes, I have a killfile. If I don't respond to something,
it's also possible that I'm busy.

in response to:

It appears that there must be a substantial number of variables that
can, individually or in combination, have an effect on the presence
and severity of the problem...but it does not appear that there is any
established methodology for evaluating the possible factors and
identifying the cause in any given case, beyond the "try this stuff
and see what works" approach.

"Shayne Wissler" wrote in message
newshteb.641533$YN5.493906@sccrnsc01...

Well this just won't do. We live in a day and age where science and
technology can answer such questions--assuming the interested parties take
interest. Maybe back in the 60's such a stance made sense, but we've got
all
sorts of fancy methods and tools for dealing with these kinds of problems.
How many physics PhD's have looked into this issue? What tests have been
run? Has there been any scientific approach at all to this issue, or is it
only individual cyclists that have built up an unscientific lore about the
shimmy?

I would assume that companies like Trek would care about whether their
products were safe, and put at least some R&D into this issue. Indeed, it
seems like a good opportunity to make some extra cash: if they figure out
the problem, and keep the answer proprietary, they can offer bikes that
are
guaranteed not to wobble. In any case, it doesn't help business to have
some
people scared out of the sport, or worse. And it doesn't help for cyclists
to take a passive stand on the issue and just accept wobbling bikes.


If a company spent money to have, as you suggest, Physics PhDs look into the
issue of shimmying bikes, do you think they would have people trolling this
group
to let us know for free what they have found out? Why wouldn't they just
produce shimmy-free bikes and not advertise that fact? Surely the number of
cyclists who have experienced shimmy and are in the market for another bike
are
a vast minority of bike shoppers. Bike consumers seem to be swayed much
more
convincingly by the visual identifiers of technical advancements than a
scientific claim
substantiated only by a guarantee.
I think that most companies of significant size have faced the shimmy issue
at one point
or another, but that it hasn't been worth the trouble to understand the
underlying cause,
since the problem bikes aren't terribly common, are less commonly exposed as
such by
their riders, and for those that do and have their cases examined, some
component change
or slew of changes typically solves the problem without needing to
understand it.
I'd very much, as I'm sure many of us would, like to know the underlying
cause well enough
to successfully predict it.
In similarity to your idea of the value in the marketplace of guarantees of
non-shimmy design,
an indivicual who did understand it completely could market their knowledge
to
manufacturers so that the manufacturers could design problem shimmy out of
their bikes.
It seems that we the interested see as much likely fruit of this labor as do
the manufacturers
to do it themselves.
There is good info in the Faq on this, there is a lot of noise and some
additional interesting
ideas in the archives of this group, and I suspect that's close to the best
anyone has done.

-Brian Smith in NY

This is basically
what smaller bicycle frames do in that their shorter main tubes have
greater torsional stiffness causing a frequency mismatch between wheel
oscillation frequency and energy stored between bound and re-bound.

Yes, that's the problem, in a nutshell.

yep. "tuning".

wrote in message
...
Shayne Wissler writes:

So to what do you attribute the change in response. The materials in
the bicycle do not change their response but the rider is a great
variable with the ability of denial of facts.

You have an average ability in ad hominems. Perhaps that works with
most people you encounter. It doesn't work on me. You know, I can
do ad hominems too, and I think I do a better job of it when I want
to. For example, what possible motivation might you have for
wanting to blame the rider at every turn? Let's see, could it be
the fact that bicycle manufacturers pay you money to testify against
injured cyclists?

Interesting twist. Where do you get that notion? You might want to
cite such a case if you want to improve your credibility.

It's not an allegation. Just an educated guess. Not unlike your ad hominems,
except perhaps that mine have more basis in fact. Perhaps if you provide
evidence for your wild assumptions about what psychological reasons caused
my shimmy, I'll provide reasons why I'd guess that you might represent
bicycle companies. But really my motive here was to attempt to get you to
cease and desist with your invalid argumentative techniques.

Nice dodge. So to what do you attribute the change in response,
considering that according to your recounting of the event, everything
was the same.

No, you're the one dodging. I answered your question.

You seem to want others to solve your problem.

You seem to want to pretend to provide answers. I'm just trying to keep the
answers honest.

But let's get back on subject. I only ask you to refrain from the ad
hominems and just present whatever scientific knowledge you might
have. If you have none then feel free to take your ad hominems
somewhere else--I'm not interested in your speculations about what
cyclist might have been shivering from what, or your psychologizing
about who might be in denial of what facts.

These considerations come from observed phenomena of riders who had
exactly these problems.

So, since rider X got scared out of his wits while shimmying, rider Y must
have been too.

You don't address why you believe these
assessments are invalid or not scientific.

Well it's pretty obvious what's wrong with the reasoning. Just because
people have the capacity to be scared, deluded, or to lie, does not imply
that a particular person is scared, deluded, or lying. As a matter of fact I
was not scared at all, and I am presenting the facts to the best of my
recollection. You can even see my polar data to see my speed just before a
rapid deceleration, with only a slight rise in heart rate, which I attribute
to the increase in the physical demands of stopping since I was not scared.

How about putting forth
some of your own ideas on the subject instead of attacking those that
have been proposed.

I did put forth a technical hypothesis actually. I also like your shopping
cart example. It's a good start.

Some of my findings arise from the time that I designed automotive
suspension for racing and sports cars at Porsche, analyzing their
response and that of motorcycles and bicycles that have some common
problems such as shimmy.

Technical credentials are good, but they aren't a substitute for a causal
explanation. And I realize that you owe no one a causal explanation.

The Tacoma Narrows Bridge is an apt example here. The bridge worked
fine in many circumstances. But there was one particular
circumstance where it failed. That was enough to call the bridge a
complete engineering failure. Civil engineers used it to learn from
past mistakes and not make them again.

Unlike your bicycle, the conditions were different. This was the
first time the bridge was subjected to a continuous wind of that
magnitude. Once it began to twist from lateral sway, it became an
oscillating air foil with angular pitch. This bridge has been dragged
into proofs of many unrelated phenomena by armchair experts. It does
not apply here.

The bridge is perfectly apt as I have demonstrated, and since nothing in the
above addresses the subject of whether it's actually apt, nor anything I
actually said, I see no reason to say anything, except to observe yet
another mediocre attempt at an ad hominem argument. Apparently the fact that
you worked for Porche is supposed to make us overlook the fact that your
main method of presenting conclusions is to insult those who disagree with
you.

A bike that works for most riders, or for most weight distributions,
or for most handlebar positions, etc., but has a drastic and
unpredictable failure mode at a particular speed etc., represents a
similar design failure.

Yes the bicycle's materials don't change. Neither did the bridge's
materials. But the conditions of the uses *do* change. And when
those conditions are in the realm of what the designer should
expect, and the bike does something radically wrong, there's
something wrong with the bike. You can't blame the rider because he
leans forward a little, or tightens his grip, and the bike starts to
radically vibrate. It may be good advice to recommend that, for a
vibrating bike, the cyclist do various things to accomodate, but
this is in order to compensate for defective behavior, not something
that the rider "should" have been doing all along.

I think Sheldon Browns item on left hand threads has some appropriate
words on this:

# Ignorant people outside the bike industry sometimes make the
# astonishing discovery that the way it has been done for 100 years is
# "wrong." "Look at these fools, they go to the trouble of using a
# left thread on one pedal, then the bozos go and put the left thread
# on the wrong side! Shows that bicycle designers have no idea what
# they are doing..."

Another ad hominem. You're really starting to bore me with this.

Steering dampers and other anti shimmy devices have not found favor
among bicyclists because the problem is neither serious enough nor the
mechanisms an acceptable alternative in cost, weight, or convenience.

IF you had provided any evidence that those are the only alternatives, then
perhaps I would be sympathetic to your points. But obviously, many bikes
don't shimmy at cycling speeds--without the aid of these devices. So there
is reason to believe that a more elegant solution to the shimmy problem is
possible. And that's really my main complaint here. You seem think that the
only alternative is some kind of clumbsy contraption, that a clever idea
isn't going to solve the problem. And in your expert status you foster an
anti-investigation attitude. Well if you have absolute proof, then fine, we
shouldn't waste our time. But history is riddled with "experts" who held a
field back because of their dogma.


Shayne Wissler

"Werehatrack" wrote in message
...
On Wed, 01 Oct 2003 16:28:14 -0400, Rick Onanian
may have said:

On Wed, 01 Oct 2003 20:10:40 GMT, "Shayne Wissler"
wrote:
Why get out of bed in the morning? Maybe you'll miss an important call
saying that you won the lottery.

Drat! I KNEW there was a reason I haven't yet won...it's because
I keep getting out of bed in the morning!

Dontcha just love people who scream "There's a problem here, and
somebody needs to fix it!", but who get all huffy when the answer is,
"Okay, go ahead."

I never demanded that anyone fix the problem.

My problem is with those who claim it isn't a problem with the bike, and/or
who say that if it is a problem with the bike then it's intractable and so
the best we can do is work around the problem. If that's their position then
I expect proof of this intractability.


Shayne Wissler